1. Field of the Invention
The present invention relates to an active noise control system for reducing second noise that is generated in a vehicle based on first noise generated by a noise source such as an engine or the like on the vehicle, with third noise that is generated as a noise for canceling out the second noise, and an active vibration control system for reducing second vibration that is generated in a vehicle based on first vibration generated by a vibration source such as an engine or the like on the vehicle, with third vibration that is generated as vibration for canceling out the second vibration.
2. Description of the Related Art
There has recently been proposed an active noise control system for detecting noise in the passenger compartment of a vehicle, which is caused by noise or vibration generated by a noise source such as an engine or the like on the vehicle, with a microphone disposed in the vicinity of the ears of a passenger in the passenger compartment, and generating a control signal based on the detected noise (see Japanese patent No. 2827374).
In the active noise control system, the control signal is output to speakers disposed in the passenger compartment, and the speakers radiate canceling noise based on the control signal into the passenger compartment for canceling out the noise at the ears of the passenger with the canceling noise.
The noise (vibration) generated by the engine as the noise (vibration) source represents periodic noise (vibration) caused by engine sounds and vibrational forces generated by the rotation of the engine output shaft. Therefore, the noise produced in the passenger compartment due to the noise (vibration) generated by the noise (vibration) source also represents periodic noise (vibration). Since the noise in the passenger compartment comprises a real component and an imaginary component, ideally, an error signal output from an ideal microphone comprises a real component (real term) and an imaginary component (imaginary term).
An actual microphone, however, is capable of detecting a real term of the noise only, and an error signal output from the actual microphone comprises a real term only. Therefore, the active noise control system which employs the actual microphone generates a control signal based on the detected real term of the noise and a reference signal.
Specifically, an ECU of the active noise control system ignores any imaginary term of the error signal, and updates the filter coefficients of an adaptive filer based on the real term of the error signal and the reference signal. The adaptive filter generates a control signal based on the reference signal using the updated filter coefficient. The canceling noise radiated from the speakers based on the control signal represents sounds depending on the real part of the error signal.
As described above, since the noise in the passenger compartment is periodic noise having certain frequencies which is made up of a real term and an imaginary term, the noise in the passenger compartment cannot reliably be reduced in a short period of time even though the canceling noise depending on the real term is radiated into the passenger compartment.
Furthermore, because the vibration from the engine as the vibration source on the vehicle is periodic vibration, the vibration produced in the passenger compartment by the periodic vibration cannot reliably be reduced in a short period of time unless the imaginary term of the vibration is taken into account.